1. Field of the Invention
This invention relates to the field of piezoelectric actuators. More particularly, this invention relates to the field of a piezoelectric actuator assembly having a wrap-around electrode and an inactive constraining layer.
2. Description of Related Art
Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit 100 includes a spinning magnetic disk 101 containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 to which a magnetic head slider (not shown) is mounted proximate the distal end of load beam 107. The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end nearest to base plate 12 which is swaged or otherwise mounted to an actuator arm. The “distal” end of a suspension or load beam is the end that is opposite the proximal end, i.e., the “distal” end is the cantilevered end.
Suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 112 that moves the suspension 105 arcuately in order to position the head slider over the correct data track on data disk 101. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the spinning disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk's surface.
Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspension are known. In a single stage actuated suspension, only the voice coil motor 112 moves suspension 105.
In a DSA suspension, as for example in U.S. Pat. No. 7,459,835 issued to Mei et al. as well as many others, in addition to a voice coil motor 112 which moves the entire suspension, at least one additional microactuator is located on the suspension in order to effect fine movements of the magnetic head slider and to keep it properly aligned over the data track on the spinning disk. The microactuator(s) provide finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which only effects relatively coarse movements of the suspension and hence the magnetic head slider. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible.
FIG. 2 is a top plan view of the prior art suspension 105 in FIG. 1. Two PZT microactuators 14 are affixed to suspension 105 on microactuator mounting shelves 18 that are formed within base plate 12, such that the PZTs span respective gaps in base plate 12. Microactuators 14 are affixed to mounting shelves 18 by epoxy 16 at each end of the microactuators. The positive and negative electrical connections can be made from the PZTs to the suspension's flexible wiring trace and/or to the plate by a variety of techniques. When microactuator 14 is activated, it expands or contracts and thus changes the length of the gap between the mounting shelves thereby producing fine movements of the read/write head that is mounted at the distal end of suspension 105.
FIG. 3 is a side sectional view of the prior art PZT microactuator and mounting of FIG. 2. Microactuator 14 includes the PZT element 20 itself, and top and bottom metalized layers 26, 28 on the PZT which define electrodes for actuating the PZT. PZT 14 is mounted across a gap by epoxy or solder 16 on both its left and right sides as shown in the figure.
In DSA suspensions it is generally desirable to achieve a high stroke distance from the PZT per unit of input voltage, or simply “stroke length” for short.
Many DSA suspension designs in the past have mounted the PZTs at the mount plate. In such a design, the linear movement of the PZTs is magnified by the length of the arm between the rotation center of the PZTs and the read/write transducer head. A small linear movement of the PZTs therefore results in a relatively large radial movement of the read/write head.
Other suspension designs mount the PZT at or near the gimbal. An example of a gimbal-mounted PZT is the DSA suspension shown in co-pending U.S. application Ser. No. 13/684,016 which is assigned to the assignee of the present invention. In a gimbal-mounted DSA suspension (a “GSA” suspension) it is particularly important to achieve high stroke length, because those designs do not have nearly as long an arm length between the PZTs and the read/write transducer head. With a shorter arm length, the resulting movement of the read/write head is correspondingly less. Thus, achieving a large stroke length is particularly important in GSA design.